The problem with fountain-pens has always been that they are prone to ink leaks as a result of changes in pressure and/or temperature. These changes occur when there is a drop in pressure in mountainous areas or on airplanes, or when passing from low temperatures to high temperatures. These changes cause the air contained in the reservoir to expand which results in a corresponding quantity of ink leaking out through the nib, if the latter is pointing downward; the greater the change in pressure, the more ink leaks out. Also, the more air is contained in the reservoir, the more ink will leak out through the nib.
In the fountain-pen's one-hundred-year-plus history, this problem has only partially been solved by attaching fins to the ink-conveying member. The purpose of these fins, which can be seen underneath the nib of any fountain-pen, is to trap small leaks and prevent them from flooding into the cap. The limitations of such a system are that the fins have a limited capacity and work effectively only with very small reservoirs, such as for example a cartridge (capacity of approx. 0.8 cc). With a reservoir of approximately 3 cc the usefulness of the fins is very limited. This problem means that the writing span of fountain-pens currently available is very short, given an average reservoir capacity of approximately 1 cc.